Element for thermal fuse, thermal fuse and battery including the same

ABSTRACT

A thermal fuse includes a first insulation film having a pair of metal terminals mounted thereto, a fusible alloy located over the first insulation film and connected between respective ends of the metal terminals, a second insulation film provided over the fusible alloy and bonded to the first insulation film as to provide a space between the first and second insulation films. The fusible alloy includes an Sn—Bi—In alloy containing 20 to 39.5 wt. % of tin, 11.5 to 31 wt. % of bismuth, and 49 to 68.5 wt. % of indium. The fusible alloy does not release lead or cadmium even after being disposed of since it contains no lead and no cadmium.

TECHNICAL FIELD

The present invention relates to an element for a thermal fuse, athermal fuse including the element, and a battery including the thermalfuse.

BACKGROUND ART

Electronic apparatuses excluding cadmium and lead are recently demandedsince it is an issue that cadmium and lead are released from theelectronic apparatuses and contaminate the natural environment. It isaccordingly desired that thermal fuses used for protection of theelectronic apparatuses are free from cadmium and lead.

Particularly in packaged batteries used in devices, such as mobiletelephones, thermal fuses that do not contain lead and cadmium aredemanded since the thermal fuses are connected to batteries by spotwelding, and lead-free solder is already used for protection circuitsfor regulating charges and discharges of the batteries.

These packaged batteries have small thermal capacities according toreducing if their sizes, and have their temperatures rising rapidly whenbeing heated. It is therefore necessary that these thermal fuses havelow fusible temperatures ranging from 85° C. to 95° C. in order to stopelectric currents quickly in case of abnormal conditions.

FIG. 7 is a sectional view of a conventional thermal fuse. Theconventional thermal fuse includes tubular insulation case 1 havingopenings at both ends, fusible alloy 2 having a substantially columnaror prismatic shape within insulation case 1, a pair of lead conductors3, flux coated on fusible alloy 2 (not shown in the figure), and sealingmember 4 for sealing the openings at the both ends of insulation case 1.Lead conductors 3 have their respective ends connected to respectiveends of fusible alloy 2, and have respective other ends extending to theoutside through the openings of insulation case 1. Thermal fuse fusibleat a temperature ranging from 85° C. to 95° C. includes fusible alloy 2made of Sn—Cd—In eutectic alloy (having a melting point of 93° C.) orSn—Bi—Pb eutectic alloy (having a melting point of 95° C.).

Japanese Patent Laid-Open Publication No.2000-90792 discloses a thermalfuse including a fusible alloy containing lead and cadmium.

Since the conventional thermal fuse uses fusible alloy 2 containing leadand cadmium, disposal of an electronic apparatus using this thermal fusereleases lead and cadmium.

SUMMARY OF THE INVENTION

A fusible element used in a thermal fuse includes an alloy containing 20wt. % to 39.5 wt. % of tin, 11.5 wt. % to 31 wt. % of bismuth, and 49wt. % to 68.5 wt. % of indium.

A thermal fuse including the fusible element does not release lead orcadmium even if being disposed of.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of a thermal fuse according to ExemplaryEmbodiment 1 of the present invention.

FIG. 1B is a sectional view of the thermal fuse taken along line 1B-1Bshown in FIG. 1A according to Embodiment 1.

FIG. 1C is an enlarged sectional view of the thermal fuse according toEmbodiment 1.

FIG. 2 shows compound of Sn—Bi—In ternary alloy for providing a fusiblealloy of the thermal fuse according to Embodiment 1.

FIG. 3A is a top view of a thermal fuse according to ExemplaryEmbodiment 2 of the invention.

FIG. 3B is a sectional view of the thermal fuse taken along line 3B-3Bshown in FIG. 3A according to Embodiment 2.

FIG. 4 is a perspective view of a battery according to ExemplaryEmbodiment 3 of the invention.

FIG. 5 is a sectional view of a radial type thermal fuse according toExemplary Embodiment 4 of the invention.

FIG. 6 is a sectional view of an axial type thermal fuse according toExemplary Embodiment 5 of this invention.

FIG. 7 is a sectional view of a conventional thermal fuse.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Exemplary Embodiment 1

FIG. 1A is a top view of a thin thermal fuse according to ExemplaryEmbodiment 1 of the present invention. FIG. 1B is a sectional view ofthe thermal fuse taken along line 1B-1B shown in FIG. 1A. Firstinsulation film 11 formed of a single-layered sheet is provided with apair of metal terminals 12 having widths narrower than that of firstinsulation film 11. Fusible alloy 13 is connected between respectiveends of metal terminals 12 and positioned over first insulation film 11,and provides a fusible element of the thermal fuse. A surface of fusiblealloy 13 is coated with flux (not shown) made of resin includingessentially rosin. Second insulation film 14 of a single-layered sheetis placed over fusible alloy 13, and bonded to first insulation film 11by sealing, so that a space is provided between insulation films 11 and14. Fusible alloy 13 is hermetically sealed by securely bonding theouter circumference of second insulation film 14 to the outercircumference of first insulation film 11 to prevent fusible alloy 13from deterioration. Insulation films 11 and 14 thus provide aninsulation housing for enclosing fusible alloy 13.

Metal terminals 12 have flat strip or filament shapes made of metalessentially including nickel, nickel-based alloy, such as copper nickel,solid nickel, or nickel alloy including other material. Metal terminals12 containing more than 98% of nickel has a low specific resistanceranging from 6.8×10⁻⁸Ω·−m to 12×10⁻⁸Ω·−m, hence having an improvedreliability including a resistance to corrosion. A thickness of themetal terminal 12 is not more than 0.15 mm. If the thickness exceeds0.15 mm, the thermal fuse becomes too thick. Since metal terminals 12are made of material having a Young's modulus ranging from 3×10¹⁰ Pa to8×10¹⁰ Pa and a tensile strength ranging from 4×10⁸ Pa to 6×10⁸ Pa, theydo not often deform accidentally during handling and transportation,hence being easily bent without breaking in a bending process. If theYoung's modulus is not larger than 3×10¹⁰ Pa, metal terminal 12 iseasily bent, hence having wavy deformation at portions which are not tobe bent (e.g., end portions of metal terminals 12 to be arranged to usefor electrical connections). This prevents the terminals from beingconnected fusible alloy 13 by welding. If the Young's modulus is notless than 8×10¹⁰ Pa, metal terminals 12 are hardly to bent and broken,.Furthermore, if the tensile strength is not more than 4×10⁸ Pa, metalterminals 12 is easily bent. If the strength is not less than 6×10⁸ Pa,the terminals are hardly bent and broken.

Each of metal terminals 12 may include metal layer 12A made of material,such as tin or copper on an upper surface at the distal end thereof, asshown in FIG. 1C. The layer provides a wettability to fusible alloy 13to ensure connection between metal layer 12A and fusible alloy 13. Sincetin and copper composing metal layers 12A have wettability to fusiblealloy 13 better than that of nickel used for metal terminals 12, tin andcopper expedite flow of melted fusible alloy 13 toward the metal layers12A, thereby facilitating disconnection of fusible alloy 13.

Materials suitable for metal layers 12A include solid metals of copper,tin, bismuth, indium, and alloys of them. Metal layers 12A preferablyhave thicknesses not more than 15[tm. If the thicknesses are larger than15 μm, an amount of metal composing metal layers 12A diffusing towardsfusible alloy 13 increases. This increase changes a melting point offusible alloy 13, hence causing a fusing temperature of the thermal fuseto shift. Metal layers 12A may be made of material having a compositionidentical to that of fusible alloy 13, and does not change the meltingpoint of fusible alloy 13 since the amount of the diffusing metalcomposing the metal layers 12A is very small even if it diffuses tofusible alloy 13.

Fusible alloy 13 is composed of Sn—Bi—In alloy which contains 20 to 39.5wt. % of tin, 49 to 68.5 wt. % of indium, and 11.5 to 31 wt. % ofbismuth. The alloy provides the thermal fuse having a fusing temperaturerated not higher than 95° C. and excluding lead and cadmium.

Fusible alloy 13 does not have a sufficient strength if a composition oftin is less than 20 wt. % in Sn—Bi—In alloy composing fusible alloy 13since indium is softer than tin, and since bismuth is more brittle thantin. As a result, it is difficult to handle fusible alloy 13 inmanufacturing processes. In Sn—Bi—In alloy containing not less than 20wt. % of tin, if a composition of indium is less than 49 wt. %, theamount of tin is excessively large. The composition of indium more than55 wt. % is excessively large. A melting point of solid tin is 232° C.,which is higher than the melting point of 156° C. of solid indium. Themelting point of fusible alloy 13 depends greatly upon the compositionof tin if the alloy contains an excessive amount of tin. Hence, avariation of the composition causes deviation of the melting point,hence causing a large change of the fusing temperature of the thermalfuse. For this reason, the composition of indium is more than 49 wt. %,and preferably ranges from 49 to 55 wt, % since these figures provide adesirable balance between tin and indium. In the case that Sn—Bi—Inalloy containing 20 wt. % of tin and 49 wt. % of indium, the meltingpoint of fusible alloy 13 exceeds 95° C. if a composition of bismuth isless than 11.5 wt. %. Therefore, the Sn—Bi—In alloy contains not lessthan 11.5 wt % of bismuth for use in the thermal fuse having the fusingtemperature rated not higher than 95° C. for protecting a battery. FIG.2 shows a composition of Sn—Bi—In ternary alloy composing fusible alloy13. Fusible alloy 13 having the above composition corresponds to an areasurrounded by line 15 in FIG. 2. The composition of indium preferablyranges from 49 to 55 wt. % corresponding to hatched area 16.

Fusible alloy 13 is processed to have a filament shape by a process,such as die drawing or die extrusion with a die having a circularcross-section. Alloy 13 of the filament shape is pressed to have arectangular or oval cross section having a thickness not more than 0.1mm. This filament shape is then cut to have a predetermined length.Fusible alloy 13 is placed between the respective ends of metalterminals 12 and at the center over first insulation film 11. Metalterminals 12 and fusible alloy 13 are connected by a process, such aslaser welding, hot welding, or ultrasonic welding. The laser welding issuitable since reducing an area to be heated for the connection offusible alloy 13 to metal terminals 12 without causing damages to areasother than welding portions.

First insulation film 11 and second insulation film 14 have thicknessesnot more than 0.15 mm. Films having thicknesses exceeding 0.15 mm arenot suitable for the thin thermal fuse since increasing a thickness ofthe thermal fuse. First insulation film 11 and second insulation film 14may be made of resin essentially including one of polyethyleneterephthalate (“PET”), polyethylene naphthalate (“PEN”), ABS resin, SANresin, polysulfone, polycarbonate, Noryl, vinyl chloride, polyethylene,polyester, polypropylene, polyamide, PPS resin, polyacetal,fluorine-base resin and polyester, and may be preferably includesthermoplastic resin.

According to Embodiment 1, first insulation film 11 and secondinsulation film 14 made of single-layered sheets are explained, and maybe made of laminated sheets of plural materials different from eachother. For example, first insulation film 11 and second insulation film14 may be composed of laminated sheets of PET film and PEN film toobtain a larger strength. This can increase a mechanical strength of thethermal fuse. In addition, laminated sheets of first insulation film 11and second insulation film 14 may be made of combination of materialshaving a low thermal resistance and a high thermal resistance,respectively, besides the combination described above.

According to Embodiment 1, a sufficient insulation distance may not beensured between metal terminals 12 after the thermal fuse is fused dueto a spine-like projection, such as a burr, left on metal terminals 12at manufacturing processes. A main body of the thermal fuse consistingof first insulation film 11, second insulation film 14, and fusiblealloy 13 has an overall length not more than 2.0 mm, as denoted byreference symbol La in FIG. 1A and FIG. 1B, and is not useful as thethermal fuse. If the length La is not less than 5.0 mm, the thermal fuseis not practical for use in a small sized battery since the fuserequires a large space for mounting. The thermal fuse preferablyincludes a main body having length La ranging from 2.0 mm to 5.0 mm.

Furthermore, if a thickness Lb in FIG. 1B measured from the bottomsurface of first insulation film 11 to the upper surface of secondinsulation film 14 is not more than 0.3 mm, the thickness is notsuitable to make a thermal fuse since the thickness does not provide aspace to accommodate fusible alloy 13. If thickness Lb not less than 0.7mm, the thermal fuse becomes too thick. If the thermal fuse is mountedto a small battery having a projection, such as an electrode, having aheight ranging from 0.5 to 0.7 mm, for example, the combination of thethermal fuse and the battery become too thick to be actually used.Therefore, the thickness Lb from the bottom surface of first insulationfilm 11 to the upper surface of second insulation film 14 preferablyranges from 0.3 to 0.7 mm.

Fusible alloys according to Embodiment 1 having predeterminedcompositions were prepared, and were examined.

EXAMPLE 1

Alloy composed of 37 wt. % of tin, 12 wt. % of bismuth, and 51 wt. % ofindium was die-drawn to have a filament shape having a circularcross-section having a diameter of 0.5 mm, is pressed to have a filamentshape having a rectangular cross section having a thickness of 0.1 mmand a width of 1.95 mm, and then, is cut to have a length of 3 mm, thusproviding fusible alloy 13 PET films having a length of 5 mm, a width of3 mm and a thickness of 0.1 mm were used for first insulation films 11and second insulation films 14. Metal terminals 12 were made of nickelplates having a length of 10mm a width of 3 mm, and a thickness of 0.1mm, and have respective end portions tin-plated to provide plated layers12A having thicknesses of 10 μm. Flux (not shown) essentially includedrosin.

EXAMPLE 2

Alloy composed of 32 wt. % of tin, 18 wt. % of bismuth, and 50 wt. % ofindium was used for fusible alloys 13. First insulation films 11, metalterminals 12, second insulation films 14 and flux were the same as thoseof Example 1.

COMPARATIVE EXAMPLE 1

Alloy composed of 40 wt. % of tin, 15 wt. % of bismuth, and 45 wt. % ofindium was used for fusible alloys 13. First insulation films 11, metalterminals 12, second insulation films 14 and flux were the same as thoseof Example 1.

COMPARATIVE EXAMPLE 2

Alloy composed of 42 wt. % of tin, 8 wt. % of bismuth, and 50 wt. % ofindium was used for fusible alloys 13. First insulation films 11, metalterminals 12, second insulation films 14 and flux were the same as thoseof Example 1.

Twenty samples of each of thermal fuses include fusible alloys 13 ofExample 1, Example 2, comparative Example 1, and Comparative Example 2.The thermal fuses have small thicknesses ranging from 0.55 to 0.70 mm.The prepared thermal fuses were placed inside an air-circulating oven,and were measured in fusing temperatures on the thermal fuses while thetemperature in the oven rose at a rate of 1° C./min.

Table 1 shows a result of the measured fusing temperatures of thethermal fuses of Example 1, Example 2, Comparative Example 1, andComparative Example 2. TABLE 1 Fusing Comparative ComparativeTemperature Example 1 Example 2 Example 1 Example 1 Average 93.8° C.86.5° C.  97.2° C. 103.1° C. Highest 94.5° C. 87.8° C. 100.6° C. 105.2°C. Lowest 93.2° C. 85.7° C.  93.2° C. 101.3° C.

As shown in Table 1, the thermal fuses of Examples 1 and 2 exhibitdifferences between their respective highest fusing temperatures and thelowest fusing temperatures not more than 3° C., hence providing thermalfuses having small variations in their fusing temperature. The thermalfuses of Comparative Example 1 includes alloy containing excessiveproportion of tin, and hence, exhibits the difference exceeding 4° C.between the highest fusing temperature and the lowest fusingtemperature, thus exhibiting large variations of the fusing temperature.In other words, the fusible alloy used in the fuse of ComparativeExample 1 is not suitable for use in the thermal fuses since exhibitingvariations exceeding 4° C. of the fusing temperature, which is a limitrequired for ordinary thermal fuses. The thermal fuses of ComparativeExample 2 have fusing temperatures exceeding 95° C. since they contain asmall amount, 8% of bismuth.

According to Embodiment 1, fusible alloy 13 made of Sn—Bi—In alloy isexplained, and may not necessarily exclude unavoidable impurities, suchas zinc, silver, copper mixed in this alloy. An amount of suchimpurities is preferably not more than 0.5 wt. % since the impuritiesmay further change the fusing temperature if included at a rate morethan 0.5 wt. %.

EXEMPLARY EMBODIMENT 2

FIG. 3A is a top view of a thin thermal fuse according to ExemplaryEmbodiment 2 of the present invention. FIG. 3B is a sectional view ofthe thermal fuse taken along line 3B-3B shown in FIG. 3A.

The thermal fuse of Embodiment 2 shown in FIG. 3A and FIG. 3B includesthe same components as those of a thermal fuse of Embodiment 1 shown inFIG. 1A and FIG. 1B. The thermal fuse according to Embodiment 2 differsfrom that of Embodiment 1 in that metal terminals 112 has a portion nearone end thereof protrudes over the upper surface of first insulationfilm 111 from the bottom surface, as shown in FIG. 3B. A structure otherthan this is identical to that of the thermal fuse of Embodiment 1.

Accordingly, in this thin thermal fuse of Embodiment 2, fusible alloy113 includes a fusible element of the thermal fuse connected betweenrespective ends of metal terminals 112 and positioned above firstinsulation film 111. The fusible element is composed of Sn—Bi—In alloycontaining more than 20 wt. % tin, more than 11.5 wt. % of bismuth, andmore than 49 wt. % of indium. Fusible alloy 113 thus contains neitherlead nor cadmium that may be released to the outside.

The thermal fuse according to Embodiment 2 includes a main bodyconsisting of first insulation film 111, second insulation film 114, andfusible alloy 113 and having an overall length Lc. If the length Lc isnot more than 2.0 mm, a sufficient insulation distance may not beensured between metal terminals 112 after the thermal fuse is fusedsince a spine like projection, such as a burr, on metal terminals 112 inmanufacturing processes, hence being not useful for the thermal fuse. Ifthe length Lc is not less than 5.0 mm, the thermal fuse is not practicalfor use in a small size battery since requiring a large space formounting it. The length Lc of the main body may range preferably from2.0 mm to 5.0 mm.

If a thickness Ld measured from the bottom surface of first insulationfilm 111 to the upper surface of second insulation film 114 shown inFIG. 3B is not more than 0.3 mm, the thickness is not suitable to makethe thermal fuse since a space enough to accommodate fusible alloy 113is not provided. The thermal fuse is too thick if thickness Ld is notless than 0.7 mm. The thermal fuse may be mounted to a small batteryincluding an electrodes having a projecting height ranging, for example,from 0.5 to 0.7 mm. The thickness makes the combination of the thermalfuse and the battery too thick, hence being not practical. Therefore,the thickness Ld measured from the bottom surface of first insulationfilm 111 to the upper surface of second insulation film 114 may rangepreferably from 0.3 to 0.7 mm.

EXEMPLARY EMBODIMENT 3

FIG. 4 is a perspective view of a battery according to ExemplaryEmbodiment 3 of the present invention. The battery includes battery unit21, thermal fuse 22, external electrode 23 of battery unit 21, andprotection circuit 24 connected electrically to battery unit 21. Thermalfuse 22 may be any of thin thermal fuses according to Embodiments 1 and2 shown in FIG. 1A through FIG. 3B. Terminal 25 of thermal fuse 22 isconnected electrically to external electrode 23 at connection point 26by spot welding or the like. Another terminal 27 of thermal fuse 22 isconnected electrically to protection circuit 24 at connection point 28by spot welding or the like. Component providing protection circuit 24are assembled in the protection circuit 24 with lead-free solder, suchas Sn—Ag base solder or Sn—Cu base solder. Thermal fuse 22 stops anelectric current from battery unit 21 when battery unit 21 produces heatexceeding a predetermined amount.

Thin thermal fuse 22 of the battery includes fusible alloy 13 includinga fusible element. The element is connected between respective ends ofmetal terminals 12 and positioned above first insulation film 11, forinstance, as shown in FIG. 1A. Fusible alloy 13 is composed of Sn—Bi—Inalloy containing not less than 20 wt. % of tin, not less than 11.5 wt. %of bismuth, and not less than 49 wt. % indium. Fusible alloy 13 thuscontains neither lead nor cadmium, hence preventing the battery fromreleasing lead or cadmium even if the battery is disposed of.

EXEMPLARY EMBODIMENT 4

FIG. 5 is a sectional view of a radial type thermal fuse according toExemplary Embodiment 4 of the present invention. In this thermal fuse,insulation case 31 having a cylindrical tube shape having a bottom or aprismatic tube shape having a bottom is made of any of polybutyleneterephthalate (PBT), polyphenylene sulfide (PPS), polyethyleneterephthalate (PET), phenolic resin, ceramic, glass, and the likematerials. Fusible alloy 32 having a substantially cylindrical orprismatic shape in insulation case 31 is composed of Sn—Bi—In alloy. Thealloy contains 20 to 39.5 wt. % of tin, 49 to 68.5 wt. % of indium, and11.5 to 31 wt. % of bismuth. The alloy allows the thermal fuse to have arated fusing tenperature not more than 95° C. and not to contain lead orcadmium.

If Sn—Bi—In alloy composing fusible alloy 32 contains less than 20 wt. %of tin, Fusible alloy 32 does not have a sufficient strength sinceindium is softer than tin and bismuth is more brittle than tin. Thiscomposition prevents fusible alloy 32 from being to handled easily inmanufacturing processes. The Sn—Bi—In alloy containing not less than 20wt % of tin is regarded as containing excessive amount of tin ifcontaining less than 49 wt. % of indium. The Sn—Bi—In alloy containingnot less than 55 wt. % of indium is regarded as containing an excessiveamount of indium. A melting point of solid tin is 232° C., which ishigher than a melting point of 156° C. of solid indium. The meltingpoint of fusible alloy 32 depends greatly upon the compounding ratio oftin if alloy 32 contains an excessive amount of tin. Hence, a variationof the compounding ratio increases a deviation of the melting point,hence changing the fusing temperature of the thermal fuse. For thisreason, the alloy preferably contains at least 49 wt. % of indium,preferably 49 to 55 wt. % of indium, thus providing a desirable balancebetween tin and indium. Sn—Bi—In alloy containing 20 wt. % of tin and 49wt. % of indium provides the melting point of fusible alloy 32 exceeds95° C. if containing less than 11.5 wt. % of bismuth. The fusible alloymay preferably contain not less than 11.5 wt. % of bismuth for use inthe radial type thermal fuse having a rated fusing temperature nothigher than 95° C. for protection of the battery.

Lead conductors 33 have respective one ends connected to respective onesof both ends of fusible alloy 32, and have respective other endsextending to the outside through an opening of insulation case 31. Leadconductors 33 having a filament shape may be made of solid metal, suchas copper, iron, nickel, alloy of them, and have surfaces plated withmetal, such as tin, zinc, bismuth, indium, silver, copper, and alloycontaining any of these metals. Fusible alloy 32 is coated with flux(not shown) which melts and removes an oxide film from the fusible alloy32 when the ambient temperature rises.

The opening of insulation case 31 is sealed with sealing member 34 madeof thermosetting resin, such as epoxy or silicone. Fusible alloy 32 andlead conductors 33 are connected by welding or ultrasonic welding.Alternatively, they are connected by having them melt with an electriccurrent.

The radial type thermal fuse of Embodiment 4 includes fusible alloy 32composed of the Sn—Bi—In alloy containing not less than 20 wt. % of tin,not less than 11.5 wt. % of bismuth, and not less than 49 wt. % ofindium, not containing lead or cadmium. Therefore, fusible alloy 32 doesnot release lead or cadmium. Lead conductors 33 having their respectiveone ends connected with fusible alloy 32 have respective other endsextending to the outside through the opening of insulation case 31. Thisstructure provides the radial type thermal fuse having a largeflexibility for an orientation in mounting it to a device, such as abattery.

EXEMPLARY EMBODIMENT 5

FIG. 6 is a sectional view of an axial type thermal fuse according toExemplary Embodiment 5 of the present invention. Tubular insulation case41 having openings at both ends thereof is made of any of polybutyleneterephthalate (PBT), polyphenylene sulfide (PPT), polyethyleneterephthalate (PET), phenolic resin, ceramic, glass, and the like.Fusible alloy 42 having a substantially cylindrical or prismatic shapein insulation case 41 is composed of Sn—Bi—In alloy. The alloy contains20 to 39.5 wt. % of tin, 49 to 68.5 wt. % of indium, and 11.5 to 31 wt.% of bismuth. The alloy provides the axial type thermal fuse having arated fusing temperature not higher than 95° C. and containing no leadand no cadmium similarly to a thermal fuse of Embodiment 1.

In FIG. 6, lead conductors 43 extends outward from the openings ofinsulation case 41. Respective ends of these lead conductors 43 areconnected to respective ones of both ends of fusible alloy 42. Theopening at each end of insulation case 41 is sealed with sealing member44.

Industrial Applicability

A fusible element for a thermal fuse according to the present inventiondoes not contain lead or cadmium, hence not releasing lead or cadmiumeven after the fuse is disposed of.

1. A fusible element for use in a thermal fuse, said fusible elementcomprising an alloy containing 20 to 39.5 wt. % of tin, 11.5 to 31 wt. %of bismuth, and 49 to 68.5 wt. % of indium.
 2. The fusible elementaccording to claim 1, wherein the alloy contains 49 to 55 wt. % ofindium.
 3. A thermal fuse comprising: first and second metal terminals;and a fusible alloy connected between the first metal terminal and thesecond metal terminal, the alloy containing 20 to 39.5 wt. % of tin,11.5 to 31 wt. % of bismuth, and 49 to 68.5 wt. % of indium.
 4. Thethermal fuse according to claim 3, wherein the fusible alloy contains 49to 55 wt. % of indium.
 5. The thermal fuse according to claim 3, furthercomprising an insulation housing for accommodating the fusible alloy. 6.The thermal fuse according to claim 5, wherein the insulation housingcomprises: a first insulation film having the first metal terminal andthe second metal terminal mounted thereto; and a second insulation filmlocated over a first surface of the first insulation film and over thefusible alloy to provide a space between the first and second insulationfilms.
 7. The thermal fuse according to claim 6, wherein the first andsecond metal terminals are placed on the first surface of the firstinsulation film.
 8. The thermal fuse according to claim 6, whereinrespective portions of the first and second metal terminals are locatedover the first surface of the first insulation film, wherein respectiveother portions of the first and second metal terminals are located on asecond surface of the first insulation film, and wherein the fusiblealloy is connected to the respective portions of the first and secondmetal terminals.
 9. The thermal fuse according to claim 6, wherein thefirst insulation film and the second insulation film provides a mainbody having a length ranging from 2.0 mm to 5.0 mm.
 10. The thermal fuseaccording to claim 5, wherein the insulation housing includes aninsulation case having a tubular shape having an opening, the insulationcase having a bottom, and a sealing member for closing the opening ofthe insulation case, and wherein the first and second metal terminalsextend through the opening of the insulation case to an outside of theinsulation case in a same directions.
 11. The thermal fuse according toclaim 5, wherein the insulation housing includes a tubular insulationcase having openings at both ends thereof, and sealing members forclosing the openings at the both ends of the insulation case, andwherein the first and second metal terminals extend through the openingsat the both ends of the insulation case to an outside of the tubularinsulation case, respectively.
 12. A battery comprising: a battery unit;and a thermal fuse including a first metal terminal connected with thebattery unit, a second metal terminal, and a fusible alloy connectedbetween the first metal terminal and the second metal terminal, thefusible alloy containing 20 to 39.5 wt. % of tin, 11.5 to 31 wt. % ofbismuth, and 49 to 68.5 wt. % of indium, the fusible alloy being fusibleby heat from the battery unit, wherein the thermal fuse stops anelectric current from the battery unit when the fusible alloy fuses bythe heat from the battery unit.
 13. The battery according to claim 12,wherein the fusible alloy contains 49 to 55 wt. % of indium.